1. Field of the Invention
The present invention generally relates to a width adjusting device for a paper web, which adjusts the width of the paper web for a printing system prior to a printing section of a rotary press. More particularly, the present invention relates to a lithographic rotary press which is equipped with at least one width adjusting device and a plurality of printing sections through which the paper web is successively passed.
2. Description of the Prior Art
A typical conventional lithographic rotary press adapted for a color printing system is, for example, shown in FIG. 3. This conventional lithographic press printing system comprises a plurality of printing sections P each of which includes two pairs of a combination of a plate cylinder PC and a blanket cylinder BC. The blanket cylinders BC of each printing section P are vertically arranged to be in contact with each other. In this conventional printing system, four sets of the printing sections P are horizontally arranged in parallel as shown in FIG. 3. A paper web W is horizontally fed into the four sets so as to pass the paper web W through the pressed space between four pairs of blanket cylinders BC, BC' to print on both surfaces of the paper web W.
Another conventional lithographic press for a color printing system is shown in FIG. 4 wherein four printing sets, each of which is composed of a plate cylinder PC and a blanket cylinder BC, are radially arranged about an impression cylinder IC acting as a common center cylinder. The blanket cylinders BC are each in contact with the impression cylinder IC to form the printing section P. A paper web W is travels around the circumference of the impression cylinder IC so that the paper web W is successively passed through the four printing sections P defined between the blanket cylinders BC and the impression cylinder IC, thereby printing on one side surface of the paper web W.
In recent years, many newspaper publishers have progressed to print newspaper in color inks and thus have demanded that such color printing be performed on many pages at a high speed and in a limited printing space.
In order to meet such demands, other conventional offset lithographic press color printing systems, is shown in FIG. 5 and FIG. 6 have been produced. Each printing section P includes two sets of a blanket cylinder BC and a plate cylinder PC which are symmetrically arranged so as to bring the blanket cylinders BC into contact with each other. A paper web W is vertically passed through the four printing sections P to print on both surfaces of the paper web W in the same manner as the above described systems. This type printing system is for example shown in "IFRA Newspaper Techniques English Edition", pp. 64 to pp. 73; April, 1988 published by INCA-FIEJ Research Association.
The paper web which is printed on is generally produced in such a manner that pulp fibers are mechanically cut and broken into fine particles; dispersed in water; dehydrated and dried; and finally adhered by hydrogen-bond to form a paper sheet. Under moisture condition, each of the pulp fibers tends to extend a little less than 1 percent in its longitudinal direction and 20 to 30 percent in its radial direction. Thus, the paper web is extended in its longitudinal and width directions by dampening and/or watering operations. Most of the pulp fibers of a general mechanically produced paper web are orientated in the longitudinal direction of the paper web, so that the paper web is remarkably extended in its width direction when exposed to moisture.
In lithographic printing systems employing dampening or watering operation in the printing section, the paper web is swelled by the dampening water. Therefore, the printed pattern on the paper web is also deformed in response to the swell of the paper web. Accordingly, in printing systems including at least two lithographic printing sections, each of which is associated with the dampening means for successively printing color images on the same paper web, the printed images formed at the first printing section is not correctly aligned with the images formed at the second and later printing sections. Accordingly, printed materials having poor quality are produced.